An indication of GM's problems is that it's replacement parts have been extremely expensive when compared to at least some other automakers. GM, to my knowledge, has never been able to reach needed agreeements with its suppliers to produce lower cost parts.
How do you know that expensive parts are not part of the strategy? Get people in the door and driving out with a new GM product that they're locked into with six year financing, especially "upside down" financing that guarantees the car will almost always be worth less than is owed on it. Since these people are now stuck with the car for over half a decade, they only have one source for parts.
Whatever buyers save on monthly payments by buying a GM versus a Honda or Toyota, they more than make up with repair costs. Keeps the service department in business, too. The dealership can afford to lose money in sales, as long as they can make it up some other way, with outrageous service costs, or huge markups on parts shipped to independant repair facilities.
And don't tell me "warranty", a GM warranty is worth little more than booty wipe.